Molded articles and coatings based on organopolysiloxanes

ABSTRACT

MOLDED ARTICLES AND COATINGS PREPARED FROM ORGANOPOLYSILOXANES HAVING OLEFINICALLY UNSATURATED ORGANIC SUBSTITUENTS BONDED TO SILICON ARE COATED WITH ORGANOSILICON COMPOUNDS HAVING SIN GROUPS THEREBY REDUCING OR ELIMINATING THE SURFACE TACKINESS HERETOFORE ENCOUNTERED.

United States Patent rm. c1. B32!) 27/28, 27/06 US. Cl. 117-1308 4(Ilaims ABSTRACT OF THE DISCLOSURE Molded articles and coatings preparedfrom organopolysiloxanes having olefinically unsaturated organicsubstituents bonded to silicon are coated with organosilicon compoundshaving SiN groups thereby reducing or elimi nating the surface tackinessheretofore encountered.

This invention is directed to a novel method for reducing or preventingthe tacky surface characteristics en countered in molded articles andcastings prepared from alkenylsiloxanes cured with organic peroxides.

Organopolysiloxane resin based materials based on siloxane polymerswhich harden and/ or cure to form nonelastomeric products have been wellknown and widely employed particularly as moldings, castings andcoatings. Such materials include formulations wherein the siloxanepolymer contains as least one olefinically unsaturated radical bondeddirectly to silicon for each ten silicon atoms present and the curingcatalyst is an organoperoxy compound.

Organosiloxane resins and resinous materials having a significantproportion of olefinically unsaturated radicals bonded to silicon in themolecule and cured with certain peroxy compounds have gained widespreaduse because they can be formulated and used in a solvent-free system(i.e. in the absence of organic solvent diluents). The mixtures inquestion can be prepared and remain stable for long periods of timeduring storage yet can be easily cured. Laminates and deep sections canbe prepared therefrom without the use of pressure. Further, the moldedarticles and coatings prepared by curing these materials exhibitexcellent mechanical properties such as high flex- ,ural strength.However, the cured molded and cast articles and coatings have beendeficient in that any surface exposed to the atmosphere during thehardening and cure sequence remains tacky. This somewhat uncured, tackysurface collects dust and dirt which is unsightly and seriously reducesthe electrical insulation properties of the cured resin.

It is the object of the present invention to introduce a novelorganosiloxane resin system based on alkenylsiloxanes cured with peroxycompounds. A further object is a method for reducing or preventing thetacky surface encountered with cured moldings, castings and coatings ofalkenylsiloxanes cured with peroxy compounds. Other objects andadvantages of this invention are detailed in or will be apparent fromthe disclosure and claims which follow.

This invention introduces a method for preparing molded articles andcoatings displaying non-tacky surfaces employing mixtures consistingessentially of (1) organopolysiloxane based materials having a ratio ofSi-C bonded olefinically unsaturated organic radicals to silicon atomsof at least 1/ and (2) peroxy curing catalysts wherein there is appliedto the surface of the molded article or coating an organosiliconcompound having SiN groups.

The organosiloxanes having olefinically unsaturated organic radicalsbonded to silicon can be any of those pre- 3,578,490 Patented May 11,1971 wherein each R is a monovalent hydrocarbon radical, halogenatedhydrocarbon radical or cyanoalkyl radical, at least one R per 10 siliconatoms being an olefinically unsaturated hydrocarbon radical, i.e.alkenyl or cycloalkenyl radicals, and n has an average value in therange from 0.9 to 2.4.

Examples of olefinically unsaturated radicals are alkenyl radicals suchas vinyl, allyl, hexenyl and octadecenyl and cycloalkenyl radicals suchas cyclopentenyl, cyclohexenyl and cyclooctadecenyl radicals. Because ofcommercial availability and cost factors, the vinyl and allylsubstituted siloxanes are preferred and vinylsiloxanes are mostpreferred. The ratio of olefinically unsaturated radicals to siliconatoms in the polymers is preferably in the range from 1/10 to 1/ 1. Thebalance of the R groups bonded to silicon can be alkyl radicals, arylradicals, aralkyl radicals, alkaryl radicals, halogenated derivatives ofthe foregoing and cyanoalkyl radicals as these terms are known in theart and as exemplified by methyl, ethyl, n-propyl, isopropyl, n-butyl,sec. butyl, dodecyl, octadecyl, phenyl, xenyl, naphthyl, phenanthryl,benzyl, beta-phenylethyl, xylyl, tolyl, 3,3,3-trifluoropropyl,chloromethyl, bromoethyl, iodophenyl, perchloroethyl and beta-cyanoethylradicals. Because of commercial availability, the R radicals preferablycontain not more than 30 carbon atoms .per radical, more commonly 1 to18 carbon atoms and the most preferred radicals free of olefinicunsaturation are methyl and phenyl radicals.

The organosiloxane polymers can be homopolymers or copolymers and canconsist of any desired combination within the limits set forth above ofunits of the formulae SiO RSiO R SiO, and/or R SiO If desired, up to 50percent of the oxygen atoms present as Si-O-Si linkages can be replacedby silcarbane linkages formed by divalent or polyvalent hydrocarbonradicals such as methylene, ethylene, and paraphenylene radicals. Theoperable siloxane polymers have viscosities measured at 25 C. in therange from about 5 cs. to 200,000 cs. with best results achieved in therange from 200 to 20,000 cs.

A preferred embodiment of the siloxane polymers employed herein arethose polymers having a viscosity at 25 C. in the range from 200 to20,000 cs. and consisting essentially of (a) 0.1 to 10 mol percent oftriorganosilyl units (-R SiO wherein the organic substituents (R) aremethyl or phenyl radicals, (b) 20 to 99.9 mol percent ofdiorganosiloxane units (R SiO) wherein the organic substituents (R") arevinyl, methyl, or phenyl radicals and, if desired, (0) up to 70 molpercent of monoorganosiloxane units (R"SiO where the organicsubstituents are vinyl, methyl or phenyl radicals, at least 1 organicsubstituent per 10 silicon atoms being a vinyl radical. In each unit,the R and R" radicals can be the same or different.

The peroxy compounds employed in the method of this invention are thoseperoxy compounds described in the prior art for use with thealkenylsiloxane polymers described above and employed herein. Suchperoxy compounds are known from and are listed, for example, in US.Pats. No. 2,934,464; No. 3,137,665; No. 2,714,099 and No. 2,894,930.Specific examples which can be mentioned herein are dicumyl peroxide,di-tert.-butyl peroxide,

cumene hydroperoxide, 2,2-bis(tert.-butyl peroxide)- butane,tert.-butylperlaurinate, tert.-butylperbenzoate, andtert.-butylhydroperoxide. These peroxy curing agents are employed instandard catalytic quantities, i.e. 0.1 to percent by weight based onthe weight of alkenylsiloxane polymer, preferably 0.5 to 3.0 percent byweight and most preferably 1.5 to 2.5 percent by weight on the statedbasis.

The novelty of the present invention is based on the use oforganosilicon compounds having nitrogen containing substitutents bondedto silicon through Si-N bonding to reduce the surface tackinessresulting from air inhibition of the cure at the surface of the coating,molding or other cured form of the siloxane-peroxy systems describedabove. The SiN containing organosilicon compounds includeorganoaminosilanes as well as organeaminosilazanes and low molecularweight siloxanes having SiN groups in the polymeric molecule. Thesecompounds are known in the art and can be prepared, for example, byreacting silanes of the general formula R,,,SiX,; where R is as definedabove, X is a halogen atom and m is 1, 2 or 3, with ammonia, primaryamines or secondary amines. Reaction with amines is preferred.

The silane reactant is generally a chlorosilane because such silanes aremost easily obtained in commercial quantities. Particularly useful aremethyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane,phenyltrichlorosilane, phenylmethyldichlorosilane,diphenyldichlorosilane, vinyltrichlorosilane, andvinylmethyldichlorosilane.

The amine reactant can be any primary or secondary amine, diamine orpolyamine. These amines can be aliphtic, cycloaliphatic, or aromatic.Examples of operative amines include dibutylarnine, ethylenediamine,cyclohexylamine, aniline, ethylamine, diethyltriamine, anddimethylamine.

The reaction between the organohalogenosilanes and the ammonia, primaryor secondary amine to produce the desired organosilicon compound havingSi-N groups is known in the art. Procedures for carrying forward thisreaction are shown, for example, in US. Pats. No. 2,462,635; No.2,564,674; No. 2,579,417; No. 2,579,418; No. 3,187,030; and No.3,143,514. It is preferred to employ sufficient ammonia or aminereactant to react with and replace all of the halogen atoms bonded tosilicon in the silane reactant. The reaction is generally carried out attemperatures in the range from about l0 C. to room temperature (about 25(3.). If silane monomers are sought, the reaction should be carriedforward under essentially anhydrous conditions, but in view of theoperability of relatively low molecular weight polymers herein theexclusion of water from the reaction zone is not required. The reactioncan be carried out in an organic solvent system wherein the solvent isinert to the reactants and reaction product. Useful solvents for thispurpose include toluene, benzene, xylene, methylene chloride,1,1,l-trichloroethane, perchloroethane, and other well-knowncommercially available organic solvents. The reactants are simplybrought into contact with each other in the solvent with mixing toassure adequate contact between reactants. The reaction is considered tobe completed when no more amine salt precipitates. The precipitatedamine salt is separated by filtration and the organic solvent is removedby distillation, under reduced pressure if desired, and the reactionproduct is thus obtained.

The organosilicon compound having SiN groups can be applied to thesurface of the molding, casting or coating prepared by heat curing theabove-described alkenylsiloxane-peroxy composition. The organosiliconcompound with SiN groups can also be applied to the molding, casting orcoating prior to heat cure with somewhat less effectiveness or employingsomewhat larger amounts of the SiN compound to achieve the desirednon-tacky surface. In general, from 0.001 to 0.05 g. of SiN containing lorganosilicon compound per square centimeter of cured siloxane resinsurface will accomplish the desired results and best results areachieved with 0.002 to 0.01 g. per

sq. cm.

The SiN organosilicon compound can be applied to the surface in anydesired manner such as by spraying, brushing, dipping, rubbing, milling,flowing and so forth. It is usually desirable to employ an organicsolvent as carrier for the SiN organosilicon compound and acetone aswell as fluorocarbon compounds which serve as carrier and propellant inaerosol packages can be employed for this purpose.

As an alternative to applying the SiN organosilicon compound to thesiloxane resin surface, one may incorporate the SiN organosiliconcompound in the alkenylsiloxane-peroxy composition formulation. However,this require the use of 0.2 to 5.0 percent by weight of the SiNorganosilicon compound based on the weight of the alkenylsiloxane peroxycompound composition, hence larger quantities of the SiN organosiliconcompound are required and this alternative is not preferred.

It is apparent from the known art that the mixture of alkenylsiloxaneand peroxy compound can also contain incidental and commonly employedadditives such as fillers or reinforcing agents including olefinicallyunsaturated pure organic compounds, as well as heat stabilizers,pigments and other additives. Examples of fillers and reinforcing agentsinclude silicas such as fume silica, silica hydrogels, silica aerogels,precipitated silicas, quartz flour, fibrous magnesium silicate, asbestospowders, fibers, papers or tissues, zirconium silicate, titania,alumina, glass powder, glass frit, glass fiber, glass yarn, glassroving, glass fabric, glass tissue, glass microspheres ground porcelainfragments (i.e. the so-called fragment flour), iron powder, aluminumpowder and metal powders, fibers and flakes as well as metal oxidepowders and flakes in general. The fillers are employed in well-knownproportions with excellent results achieved employing 35 to 900 percentby weight of filler calculated on the weight of the organopolysiloxanesemployed. Examples of olefinically unsaturated organic compounds whichcan be employed include divinylbenzene and triallylcyanurate. Theolefinically unsaturated organic compound can be employed in proportionsof from 5 to 20 percent by weight based on the mixture oforganosiloxane, peroxy compound and olefinically unsaturated compound.In addition to the peroxy compound employed as a curing catalyst asnoted above, the mixtures can contain further free-radical formershaving lower activation temperatures and decomposing more rapidly thandicumylperoxide such as, for example, tert.-butylperoctoate and benzoylperoxide.

The mixture of alkenylsiloxane and peroxy compound is cured according toknown curing and hardening schedules but excellent results are achievedheating the mixture to a temperature in the range from to 220 C. for aperiod of from 1 to 24 hours. Gradually increasing temperatures over aperiod of time are typically employed.

The method and materials of this invention find particular use forembedding electrical apparatus, impregnating electrical coils,transformers and other apparatus, in the preparation of glass fiberreinforced molded articles and in the preparation of release coatingsbased on siloxane polymers.

The following examples are included herein to assist those skilled inthe art to better understand and practice this invention. The scope ofthe invention is delineated in the appended claims and is not limited bythe examples.

EXAMPLE 1 (a) To a solution of 6.5 mol mono-n-butylarnine and 10 l.methylene chloride, there was added dropwise 1 mol ofmethyltrichlorosilane while stirring. The temperature of the solutionwas held at +10 C. After the chlorosilane had been added, the mixturewas stirred for another two hours at room temperature. It was thenfiltered off from the amino salt. The methylene chloride and excessamine was distilled off from the filtrate excluding atmosphericmoisture. The residue was a fluid consisting essentially ofmethyl-fris-(n-butylamino)silane.

(b) A linear organopolysiloxane consisting essentially of 34 mol percentdiphenylsiloxane units, 25 mol percent dimethylsiloxane units, 34 molpercent vinylmethylsiloxane units, 4 mol percent phenylmethylsiloxaneunits and 3 mol percent trimethylsiloxane units having a viscosity ofabout 5,000 cs. at 25 C. was mixed with 2 percent by weight calculatedon the weight of the organopolysiloxane of dicumylperoxide at 80 C. andthe mixture was poured into a square aluminum box with an insidemeasurement of 4 cm. by 4 cm. by 1.5 cm. open at the top and used as amold. The mold filled with this material was left to stand for 6 hoursin an air circulating oven running at 150 C. A solid glass-like moldedarticle was formed. The surface of the molded article which was exposedto the air during the curing was very tacky. This tacky surface wascoated with 0.5 ml. of a solution of 1 part by weight of the fluidconsisting essentially of methyltris(n-butylamino)silane prepared in (a)above in 3 parts by weight acetone. Within 10 minutes the acetone hadvaporized and the surface was completely tack free. A piece of filterpaper applied with a finger fell from the surface by itself withoutleaving impressions or fibers on the surface of the molded article.

EXAMPLE 2 (a) To a solution of 5.5 mol diethylamine in 10 1. of watersaturated toluene, there was added dropwise 1 mol ofphenyltrichlorosilane while stirring. The temperature of the solutionwas kept at +10 C. After the chlorosilane had been added, the mixturewas stirred for another two hours at room temperature. It was thenfiltered off from the amine salt and from the filtrate the toluene wasdistilled off at 12 mm. Hg absolute and a heating bath temperature of 50to 80 C. The residue was a fluid consisting of a low polymericphenyldiethylsilazane.

(b) A branched organopolysiloxane consisting of 30 mol percentdiphenylsiloxane units, mol percent monophenylsiloxane units, 20 molpercent dimethylsiloxane units, 5 mol percent monomethylsiloxane units,25 mol percent vinylmethylsiloxane units, mol percent monovinylsiloxaneunits and 5 mol percent trimethylsiloxane units, with a viscosity of150,000 cs. at 25 C. was mixed with 2 percent by weight calculated onthe weight of the organopolysiloxane of dicumylperoxide at 80 C. andpoured into the form described in Example 1. The mold filled with thismaterial was heated for 3 hours at 150 C. followed by 3 hours at 200 C.A solid, rigid molded article was formed. The surface of the moldedarticle which was exposed to the air during the curing, was still verytacky. The molded article was then dipped into a solution of 1 percentby weight of the low polymeric phenyldiethylsilazane prepared in (a)above in 4 parts by weight acetone for 30 seconds. Within 10 minutes theacetone had vaporized and the surface was completely tack free. Uponrubbing with a piece of cotton, no fibers adhered to this surface.

EXAMPLE 3 (a) The procedure according to Example 1(a) was repeated withthe alteration that in place of the 6.5 mol butylamine, 6.5 molmonocyclohexylamine was used. A fluid was obtained consistingessentially of methyltris- (cyclohexylamino) -silane.

(b) An organopolysiloxane consisting of mol percent diphenylsiloxaneunits, 10 mol percent phenylmethylsiloxane units, 15 mol percentdimethylsiloxane units, 30 mol percent vinylrnethylsiloxane units, 4 molpercent monophenylsiloxane units, 3 mol percent monomethylsiloxaneunits, 8 mol percent monovinylsiloxane units, and 10 mol percenttrimethylsiloxane units having a viscosity of 15,000 cs. at C. was mixedwith 400 percent by weight calculated on the weight of theorganopolysiloxane of zirconium silicate and 2 percent by Weightcalculated on the weight of the organopolysiloxane of dicumylperoxide atC. and poured into a form such as described in Example 1. The formfilled with this material was heated for 3 hours at C. followed by 3hours at C. and 3 hours at 210 C. A solid rigid molded article wasformed Whose surface exposed to the air was still tacky. This surfacewas then wiped off with a non-linting cloth which had been saturatedwith a solution of 1 part by weight of the fluid consisting essentiallyof methyl-tris-(cyclohexylamino)-silane prepared in (a) above in 3 partsby weight acetone. Within 10 minutes the acetone had vaporized and thesurface was completely tack free.

EXAMPLE 4 (a) The procedure according to Example 1(a) was repeated withthe alteration that in place of the 1 mol methyltrichlorosilane, 1.5 moldimethyldichlorosilane was used. A fluid was obtained consistingessentially of methylbis n-butylamino -silane.

(b) An organopolysiloxane of the type described in Example 3 was mixedwith 2 percent by weight calculated on the Weight of theorganopolysiloxane of dicumylperoxide and 2.5 percent by weightcalculated on the Weight of the organopolysiloxane of the fluidconsisting essentially of methylbis-(n-butylamino)-silane at 80 C.prepared above and poured into the form as described in Example l. Theform filled with this material was heated for 4 hours at 150 C. A solidrigid molded article was obtained whose surfaces were completely tackfree. No finger marks remain on the surface of the article exposed tothe air during the curing.

That which is claimed is:

1. A method for treating the surface of an organosiloxane coating ormolded article prepared by heat curing a mixture consisting essentiallyof (a) 100 parts by weight of an organopolysiloxane of the general unitformula IhSiO where each R is a monovalent radical selected from thegroup consisting of hydrocarbon radicals, halogenohydrocarbon radicalsand cyanoalkyl radicals, n has an average value of 0.9 to 2.4, at leastone R per 10 silicon atoms being an alkenyl or cycloalkenyl radical,said organopolysiloxane having a viscosity at 25 C. not exceeding200,000 cs. and (b) 0.5 to 3.0 parts by weight of an organic peroxycompound curing agent comprising ap plying to the surface of saidcoating or molded article (c) an organosilicon compound having SiNgroups and prepared by reaction of a silane of the general formula R SiXwhere R is as above defined, m is 13, and X is a halogen atom withammonia or an aliphatic, cycloaliphatic or aromatic primary or secondaryamine or polyamine, said reaction being carried forward in an inertorganic solvent at a temperature not exceeding room temperature.

2. The method of claim 1 wherein the organopolysiloxane is a copolymerconsisting essentially of (a) 0.1 to 10 mol percent of units of theformula R SiO where R is a methyl or phenyl radical, (b) 20 to 99.9 molpercent of units of the formula R SiO where R" is a vinyl, methyl orphenyl radical and (c) any other units present being of the formulaR"SiO where R" is as above defined, said organopolysiloxane having avinyl to silicon ratio in the range from 1/10 to 1/1 and a viscosity at25 C. of from 200 to 20,000 cs.

3. The method of claim 2 wherein the organic peroxy compound curingagent is selected from the group consisting of dicumylperoxide,di-tert.-butylperoxide, cumene hydroperoxide, 2,2bis(tert.butylperoxide)butane, tert.- butylperlaurinate,tert.-butylperbenzoate, and tert.-butylhydroperoxide.

4. The method of claim 1 wherein the 'organosilicon compound having SiNgroups is prepared by reacting a hydrocarbylchlorosilane of the formulaR SiCl where R is a monovalent hydrocarbon radical and m is 1, 2 or 3with at least m moles of ammonia, primary aliphatic or aromatic amine orpolyamine or secondary aliphatic or aromatic amine or polyamine wherebysubstantially all of the chlorine atoms are removed from the siliconatom.

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